Receiver shunt



A. B. CLARK ET AL Dec, 8, 1925- RECEIVER SHUNT Filed Sept. 8, 1923 s @om a. my ha, r. m

l A TTORNE Y CII Patented Dec. 8, 1925'.

JNTED STATES PATENT OFFICE.

ALVA B. CLARK, OF BROOKLYN, NEW YORK, AND GEORGE CRISSON, OF HACKENSACK, /NEW JERSEY, ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY,

A. CORPORATON OF NEW YORK.

RECEIVER SI-IUNT.

Application filed September 8, 1923. Serial No. 661,655.

To @ZZ-10710111 t may concern.' l

Be it known that we, rinvii B. CLARK and GEORGE Caisson, residing at Brooklyn and l-lackensack, in the counties of Kings and Bergen and States of New York and New Jersey, respectively, have invented certain Tmprovements in Receiver Shunts, of which the following is a specification.

This invention relates to transmission measuring devices and particularly to that form of such devices known as` a receiver shunt.

A receiver shunt is a. device which may be connected between a circuit and a telephone receiver or other receiving apparatus in order to reduce the current entering the receiver. in any desired and predetermined ratio.

A receiver shunt consists of aninipedance element in series with the receiver and one in parallelwith-it, which are varied simultaneously in order to secure the result nientioned above. Such a shunt has associated with it a calibrated dial which indicates the loss produced by it in miles of standard cable.

In the use of a receiver shunt of the type heretofore known in the art, certain errors of measurement .have been'introdueed, due to the assumption that the impedance of the telephone receiver is pure resistance. For the sake o-f simplicity of construction it has been the practice to assume that the iinped- 'l ance of the receiver is a pure resistance and to proportion the series and shunt. elements of the receiver shunt to produce the desired reduction of the current in the receiver at each step and at the same time to keep the impedance of the receiver and receivershunt together constant and equal to the assumed value of the receiver impedance. If this assumption were true the accuracy of the shunt would not depend upon the impedance of the circuit to which it is connected even if it were different from that of the receiver because the current taken by the combina.- tion of receiver and shunt would not depend upon the setting of the shunt. In the past where great precision was necessary it has been customary to associate auxiliary impedance elements, sometimes called pads,-

with the receiver which cause the combina-1 tion of receiver and pad to approximate a pure resistance. This practice increases the cost of the apparatus and wastes part of the electrical power that would otherwise be available to actuate the receiver. lVhen pads are not used there is al loss at the junction between the receiver and the shunt which depends upon the impedance of the receiver and the impedance presented by the shunt and the rest of the circuit toward the receiver. Since, as pointed out above, the latter impedance varies with the setting of the shunt this loss varies with the setting` and causes the effect of the shunt to be different from the value calculated on the assuniption mentioned above.

In our invention the shunt is used in connection with an artificial line whose impedance is a constant pure resistance and is so designed that the impedance presented toward the receiver is a constant pure resistance equal in value to that of the line. Since the impedance presented toward the receiver does not vary with the setting of the shunt the loss at the junction due to the fact that the impedance of the receiver differs from that of the shunt likewise is constant. The change in the receiver current caused by changing the shunt is therefore accurately equal to the change the shunt was designe-d to give and there is no error due tothe impedance of the receiver differing from that which it faces. In this way accuracy is attained without the expense and power losses that would be pro-A duced by padding, and the necessity of using receivers having a particular value of impedance is avoided.

It is the object of this invention to provide a shunt which, when combined with the line-circuit and the telephone receiver in a manner set forth hereinafter, will produce greater accuracy of measurement than heretofore attained.

This invention will be clearly understood from the following description when read in connection with the attached drawing, of which Figure 1 shows an electrical network involving the type of shunt heretofore used; Fig. 2 fshows a network involving an irnproved type of shunt, and Fig. 3 shows the use ofthe improved type of shunt in acircuit for measuring the transmission gain produced by a telephone repeater.

In the network shown in Fig. 1, a source ofp'otential 1 is bridged across the network litt' so as to transmit therethroi'ighcurrent of predetermined frequency. The line circuit represented by 2 is assumed to have an impedance ZL' The receiver shunt" Sil Comprises a series element/r1 and a shunt element r2. The magnitudes of the parts of the series and the shunt elements effectively t x Fig; l, which errors arise from the reactconnected with the network, may be varied by the simultaneous movementof'vthe Contact points 3 and l by means ot' the arm 5. Connected in paralleli with the shunt element,

is aI telephone receiver or other receiving` apparatus (i, whichis assumed tofbe pure resistance R. The series resistancerlvaries in such way that the impedance of the'v shunt and the current entering it are constant. This current divides between the shunt resistance r2 and thereceiver iinpedL ance R, consequently-the loss ratio produced by the shunt is where n is the current ratio' corresponding" From' the foregoing? discussion it will 'be' seen that neither the design`n0r yperformance of the typ'eoffreceiver shunt shownin Fig. l dependsupon Z,.they circuit impedance. Any reflectioiidoss'between Hand Z is constant'fat all settings of the vshunt and is lnot .included in the loss indicatedby tlie shunt.

The errors in such type'vofshuntlare as? follows: Sincethe impedaiieeofa telephone receiver is not a pure resistance Rf certain errors occur in usigcthe'sl'n'int.

.is chosen which approximateslthe receiver impedance at 1000 cycles. lThe impedance presented to the line andthe currei'itv entering the shunt therefore va'ry` with the settingof the shunt.l The impedance present-V ed by the shunt toward the receiver deV creases as the loss isincreased. Because off this and the change ot the receiverimpedance vwith frequencyl the loss caused;- bythe* shunt tends to be less thanthe indicated value at fieqi'ieiic'ies-.'below.A 1000 cycles andA greater at higher frequencies. VVh'en an iin` pfure testing currenty isused this' action causes the quality of the sound heard in Botlrthe' resistance and reactance of a receiver in-J, crease with frequencyhence a value of'R' the receiver to vary Withfthe setting of the shunt because the loss caused to the fundamental of the testing current is different from the lossencountered by Vthetharin'onics.

A method that has been suggestedforfcorrectingfthe errorsarising from the use of the type of shunt shown for example in ance., effect ofthe receiver 6, consists in inserting a network or pad between the shunt per se and the receiver, which padcoiisists- 'of'iinpedance elements so proportioned'that' the impedance of thei'eceivei',andthe pad together is a pure resistance Rl Thisarrangement,.'howev'er,- introduces a loss between the shunt andthe receiver which is objectionable because it tends to makejthe sound in the receiver -too faint for accurate comparison o f volumes.

Our invention consists in an'improveinent upon the type of shunt heretofore used whereby not only mayv the errors arising frointhe use of that type of shunt be eliminated butl also the reduction in efliciency incidental tothe use ofV a padfasl mentioned above mayv be avoided..

Since the artiiicial lines used in repeater testing circuits may be made up 'of pure resistance elements`r it has been found 'that the errors present in the earlier type of re-J ceiver shunt could be-eliminat'ed by provid` ing a shunt whichhas constant impedance' for all settingswhen viewed from thetel'ephone receiver. Our inventionconsists'not` only, in a receiver shunthav-inga constant impedance Vwhen viewed from the receiver but alsointhe combination of ashuntfhaving, the characteristic in'ention'edabove in combination with other apparatus comprising'ga repeater testing circuit.

This improved type vof shunt is sho-wn' schematically inFi'g; 2 and in detail inconne-ction with a repeater testing circuit in` Fig. 3. lnzF'igQ asource 1 of'sinus'oid'al alternating.potential is connected across' an artificial line, theelements ofV which iarecpure resistance. The opposite terininalsofthis artificial line ,are connectedv with the 're ceivershunt B1comprising afseries element' 3' anda shuntelenient et haviiigfresistai'ices` r1 andrr2 respectively. The shunt B1 is'sol designed as to have'consta'nt, impedanceifor all settings when viewed fromtlie receiver. Since the impedance of the artificial. linef'is always pure resist-ance R, the loss-causedlby they shunt'will always be that indicated by the reading of the dials associated with' the' shunt.

The manner in whichv a receiver'shunt'in combination with an artificial line of'puie resistance may bepractic'ally used is vshown in Fig.' 3, which vrepresents 'a testingcircuit fordete'rmining the gain attainedby the use`ofa repeater. NIn thisfigurelthe source of testing el'ectroinotive forcey l0 is effec-v 130 llu tively connected across the sides of the artificial line, the elements of which, 13 and 14, are pure resistances having a 'definite value. Interposed between the source and the said artificialline is a simple type of filter' consisting of an inductance 11 and a condenser 12, which are so proportioned as to transmit readily the fundamental frequency pro-duced by the source 10, and to suppress the harmonics of this frequency. The opposite terminals of the artificial line are connected with the armatures 15 and 15 of the relay 16. One terminal of the winding of this relay is connected with a source of potential 19 and the other terminal thereof is connected with a contact of the key 37. The outer contacts of relay 16 are connected with conductors leading to the input side of the repeater which may be of any well known type.A The inner contacts of the relay 16 are connected by the conductors 39 with the inner contacts of relay 21. Connected between contacts 17 and 17 of this relay is a network 18 which serves to prevent singing of the repeater when the repeater is disconnected from the source 10 and the measuring circuit (to be described later). Outer contacts of relay 21 are connected by conductors with the output side of the repeater 2O and the armatures 22 and 22 of the said relay are connected with terminals of an artificial line interposed between the repeater and the receiver shunt. A network 24 similar to 18, is connected between contacts 23 and 23. A source of potential 25 is connected with one terminal of the Winding of relay 21, the other terminal of which is connected with the same contact of key 37 with which the corresponding terminal of the winding of relay 16 is connected. The artificial line comprises a plurality of pure resistances 26 and 27 having a predetermined value. This artificial line is connected with receiver shunt which comprises the apparatus shown within the dotted rectangular space. The resistances 28 an'd 29 ma be effectively connected or disconnected, as shown by the dotted lines) depending upon the character of the artificial line used, that is, whether it simulates heavy, medium or non-loaded real lines. The resistances 30. and 31 represent respectively, the shunt and series resistances of the receiver shunt. The resistances 32, 33, 34 and 35 may be effectively connected or disconnected from the shunt circuit, depending upon the position of the key 36. The object of these resistances is to increase the range of loss through which the receiver shunt may be operated. Receiver 38 is also connected with the receiver shunt. The keys 37 and 37 are designed respectively to cut out the receiver shunt and to operate the relays 16 and 21 in order to disconnect the repeater.

The manner in which this circuit operates is as follows: The testing potential of predetermined frequency, would be applied across the artificial line, made up of the resistances 13 and 14; the current resulting therefrom is amplified by the repeater 20 and the resultant potential would cause current to flow through the artificial line, made up of resistances 26 and 27, through the receiver shunt to the receiver 38. The keys 37 and 37 would then be operated. By the operation of key 37, the series elements of the receiver shunt would be shunted out by the conductor 40. By the operation of key 37 relays 16 and 21 would be operated by the flow of current from the sources 19 and 25 to ground at key 37. Key 37 also opens the branches of the shunt in which are located the shunt elements 30, 32 and 34.

The source of potential 10 would the-n be connected through the first artificial line, thence over conductor 39 through the second artificial line to the receiver shunt and the receiver 38. The volume of the tone given by the receiver 38 under the latter condition, will be different from the volume produced when the repeater is connected in the circuit. Accordingly, the keys 37 and 37 are restored to their normal position and the receiver shunt is adjusted to cut down the volume of the tone given in the receiver. By alternately connecting' and disconnectingI the repeater and by adjusting the shunt, the volume produced when the repeater is connected into the circuit will equal that when it is disconnected. This adjustment of the receiver shunt is effected by varying the resistances 30 and 31 and also by manipulating the key 36 which, when operated in one direction, connects into the receiver shunt one series and one shunt element having an impedance of different magnitude from that which may be connected with the receiver shunt when the key is operated in the opposite direction. It would, of course, be possible to make a receiver shunt having only one series and one shunt element such as 31 and 30. If, however, the range of the receiver shunt is great the switching arrangement necessary for one series and one shunt element is quite complex. It has accordingly been found desirable to use a plurality of series and also of shunt elements. Thus, for example, the elements 30 and 31 may be designed to measure from Zero to ten miles of standard cable r dials of the receiver shunt is the gain produced by using the repeater.

llO

lVhile thisfinventien has been disclosed embodiment in other and different forms without departing-from the spirit and scope -of the appended claims.

That is claimed is:

l. In a transmission measuring system, the cen'ibination with a line circuit, the impedance- Ot which is substantially pure resistance et' a source of"alternating,current connected therewith, a telephone receiver and a. variable receiver shunt connectedv between the said artilicial line and said receiver adapted to vary the current in the said receiver, and having constant impedance when. viewed troni the said receiver'.

2. In ai transmission measuring,` system, the combination with a source of alternating current ot predetermined frequency, et 'frequency selecting means cennectedwith said source and designed to transmit current of a` predetermined frequency, an artificial line ofpure resistance connected with the said frequency selecting means, a telephone receiver, and a variable receiver-shunt connected between the said artilicial line and said receiver adapted te vary` the current in the said receiver and having a constant 30 impedance when -viewed VAtroni thel said receiver.

3. in. a receivery shunt, the -cembination with alinecircuit Of substantially pure resistance having a source of alternatingvpo- 36 tential connected"therewith cfa receivingy device, andv a variable shunticomprisinga Series and a. shunt resistance elementiconnectml betwcenthe said circuit andthesaid receivingdcvice adaptedto vary the current in the said device and havinga constant i1n pidancc whenviewed*trointhe said receiv ingr device.

1i. rlhe combination with. a. reeeiverof a variable receiver shunt connected therewith, comprising a. series resistance element and a shunt resistance elcmentfadapted t0 vary the current in the saidreceiver, yandso pro-fV portioned that the impedance ofthe said shunt is always constant when viewed from 50 the-said receiver;

ln testimony whereot', we have signed our names t0 this specification this 6th dayot' September 1923-- nLvir B. CLARK; Geenen caisson. 

